**Author details**

sunrise line. Additionally, the measured data after 6 o'clock does not change too much since process of sunrise passed. Taking into account that the difference between calculated data and the measured data is resulted from the applied models and specific measuring conditions, such as the time, locations, and propagation paths, the proposed computational scheme would be more helpful by adjusting it into more practical models than a simple structure with abrupt discontinuity in

*The magnitudes of the field component* Er *in dB versus the propagation distance due to sunrise in nighttime, daytime, and transition range, respectively, at the operating frequency* f ¼ 10 *kHz; ε*<sup>g</sup> ¼ 80*, σ*<sup>g</sup> ¼ 4 *S/m,* hN ¼ 90*km, and* hD ¼ 70*km, with (a) the simulated results comparing the transition path in N-to-D with daytime and nighttime propagations and (b) the calculated result comparing with experimental data,*

*Electromagnetic Propagation and Waveguides in Photonics and Microwave Engineering*

In this chapter, the effect of multimode interferences is investigated for VLF radio waves due to sunrise and sunset based on an idealized cascaded anisotropic inhomogeneous terrestrial waveguide. The coefficients of mode conversion for scattered vectors and transmitted vectors are evaluated at the junction of abrupt discontinuity representing the nighttime and daytime transition. The treatment provided can be enhanced in the future by a more practical terrestrial waveguide with varying effective ionosphere height rather than the abrupt one. The study may provide with some help in the applications of long-distance communication and

The authors are grateful to all referees for their constructive comments and suggestions in improving the quality of this chapter. The authors thank all associate

editors very much for their help and encouragements.

No potential conflict of interest was reported by the authors.

height boundaries.

**Figure 10.**

*respectively.*

**4. Conclusions**

navigation.

**Acknowledgements**

**Conflict of interest**

**138**

Ting Ting Gu<sup>1</sup> and Hong Lei Xu2 \*

1 Department of Information Science and Electric Engineering, Zhejiang University, Hangzhou, China

2 Science and Technology on Electromagnetic Scattering Laboratory, Beijing, China

\*Address all correspondence to: xhl\_207@126.com

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
